The present invention relates to a moisture impervious sheet particularly suitable for environmental pollution control as a water barrier for the building of ponds, lagoons and as a soil sealent for hazardous or nuclear waste having a flexible non-biodegradable support capable of venting gas and coated with an adhesive and water swellable bentonite in such a manner so as to retain its flexibility.
Various rigid panels useful in construction have been defined in prior U.S. Pat. Nos. 3,186,896; 4,048,373; 4,070,839; and 4,139,588 granted to Arthur G. Clem relating to panels and utilizing bentonite to form water barriers. In another U.S. Pat. No. 4,209,568, issued to Arthur G. Clem, there is disclosed a bentonite containing gelled oil waterproofing composition which is useful for coating the walls of various constructions to provide waterproof barriers. However, the instant invention is concerned with providing waterproof barriers for ponds, lagoons and hazardous waste sites. These present particular problems in the fact that they are extremely large areas and may be subjected to extreme forces, pressures and movement. Under such conditions rigid construction materials would be too hard to work with and extremely difficult to maintain.
Some waste matter from industrial operations is noxious, hazardous or toxic. The full listing is too large to include, but some samples would be uranium tailing, spend radioactive matter, acid metal salt solutions and the insoluble lime salts thereof, metallic pigments, acidified sludges from crude oils, spent lubricating oils, solvents, paints, polychlor biphenyls, DDT, and similar poisons. Many of these are insoluble or sparingly soluble in water. But waste acids from some waste sources could inter-react with some insoluble metal waste to generate a toxic metal solution leachate.
Leachate from hazardous waste must not enter the groundwater supply. If it does, large sources of drinking water may be contaminated for lengthy periods of time. For this reason, hazardous waste is sometimes stored in clay mines with three meters or more of native clay below the waste material.
More frequently, the soil at the waste disposal site may be permeable to some degree. If "clay" soil is available, it may be moved into the site, spread, disintegrated and moistened to the condition of maximum compactability, then rolled or temped in fifteen cm to twenty cm layers to form an impermeable surface. The surface cover may be in the sixty to one hundred centimeter thickness range. A simple calculation will show that this cover coat will significantly reduce storage volume, or will require extra earth excavation to maintain the original design volume.
If native clay soil is not present, or cannot be moved into the landfill site, one method of sealing soil has been that of a plastic sheet, laid on the ground, with seams overlapped and welded or cemented. Plastic sheets or films have many problems. Some are sensitive to ultraviolet light, and must be protected by a layer of dirt. Sheets must be joined in the field and there is a potential for leakage at each seam. Many plastic films are destroyed by hydrocarbons reducing the number of waste products that can be stored. Also, leaking organic matter passing through pinholes in the plastic liner may cause gas which will cause the liner to rise. If the liner rises it will usually tear or break and destroy the seal or waterproofing of the contaminant.
Porous soils may be sealed with colloidal bentonite to store hazardous waste. The bentonite is spread over the surface intimately mixed with soil to a depth of ten cm, moistened to optimum moisture, remixed and compacted. This too has limitations. The resulting mixture must be uniform or some zones will leak while others will be highly impermeable.
In accordance with the present invention, a method and product are provided which will allow formation of a flexible sheet with waterproofing qualities and which is suitable for use over large areas by covering the soil or other areas with the treated sheet.